Historically, ground roast coffee packaged in a can has been vacuum packed. Recently, it has been found desirable to freshly package roast ground coffee in cans or other rigid or semi-rigid gas impervious packages under atmospheric pressure as contrasted to the prior vacuum packaged cans. Additionally, it has also been found desirable to close off the top of the can with a flexible peel-off easy opening seal or lid, whether the coffee was packed under a vacuum or atmospheric pressure. Examples of such peel-off easy opening lids are shown in the Bolton et al U.S. Pat. No. 5,688,544.
Packaged ground roast coffee gives off carbon dioxide which, in a sealed confined space will generate a pressure buildup within the container. In the case of vacuum packed ground roast coffee, this generation of carbon dioxide causes no problem because the pressure buildup simply tended to reduce the negative pressure within the sealed container. However, if the product is freshly packaged initially at atmospheric pressure without extensive degassing, then generated carbon dioxide will cause a pressure buildup in the can above atmospheric pressure. In atmospheric pressure packed ground roasted coffee cans now on the market, this pressure buildup caused by the generated carbon dioxide is dealt with by simply placing a vent valve in the top of the can. If the can is of a type having a flexible peel-off seal, the vent valve will be built directly into the flexible peel-off lid.
It is also highly desirable, if not a commercial necessity, to include with any coffee can a plastic overcap which is intended primarily to protect the coffee product within the package after the main airtight seal has been opened.
A problem has developed, however, in the case of a ground roast coffee can having a vented peel-off lid and a plastic overcap. It has been found that as the gas pressure builds up within the can it tends to dome the flexible lid upwardly and eventually against the overcap. This creates several problems. First, the constant extension of the flexible lid in its domed condition deforms the flexible lid, causing a wrinkled appearance which is unacceptable to the consumer. Additionally, the materials used to seal the vent valve to the lid, including silicon-based oils, would tend to be expelled from the valve opening and onto the surface of the overcap. This causes a visual blemish which is also unacceptable to the consumer. Additionally, if the valve is sufficiently blocked, the gas within the can can cause the can itself to bulge outwardly, which again is unacceptable to the consumer.
While a primary problem has been blockage of the vent valve in the flexible easy-off lid, an additional problem arises in that gases which do escape through the lid may not be able to escape from the space between the lid and the overcap. It is true that the overcap is simply snapped over the chime of the can in a non-airtight manner. However, the surfaces of the overcap which engage the chime of the can, generally along the top and outer periphery of the chime, while not forming a hermetic seal, clearly form a closure which resists escape of any generated gases which might exit from the vent valve into the space between the lid of the can and the overcap.
Thus, a need exists for an improved arrangement for venting gases created within a can wherein the product is packed under atmospheric pressure and is of the type which generates gases sufficiently to cause a pressure buildup, especially when such a can is used in combination with an overcap.